1. Field of the Invention
The present invention relates generally to a doping process for silicon films using Molecular Beam Epitaxy (MBE) and, more specifically, to a novel boron doping source for silicon MBE.
2. Description of the Prior Art
SILICON MOLECULAR BEAM EPITAXY (N ON N+) WITH WIDE RANGE DOPING CONTROL. Ota, Yusuke, J. Electrochen. Soc. 1977, 124 (11), 1795-802. Si single-crystal films were prepared by the molecular beam epitaxy technique in a ultrahigh vacuum. Sb-doped epitaxial films were grown on Czochralski grown n+ (p.ltoreq.0.003 .OMEGA.-cm) (111) or (100) substrates from 600.degree. to 1050.degree.. The doping of the films was controlled from high 10.sup.13 to high 10.sup.17 /cm.sup.3. The p-type epitaxial film on n+ substrate were also gown from a B-doped source. Transmission electron microscopy and preferential dislocation etching revealed that the epitaxial films are high quality single crystals with low dislocation. The electrical properties on the epitaxial films are bulklike. The p+-n-n+ diodes were fabricated on these films and they showed low reverse leakage current and sharp breakdown. These diodes operate excellently at mm wave frequencies.
ENHANCED STICKING COEFFICIENTS AND IMPROVED PROFILE CONTROL USING BORON AND ANTIMONY AS COEVAPORATED DOPANTS IN SILICON-MBE. A. A. Kubiak et al. J. Vac. Sci. Technol., B 1985, 3(2), 592-5. Inefficient doping and poor profile control are generally associated with the use of coevaporated dopants in Si MBE. However, two new techniques were developed, one applicable to p-type and the other n-type doping, which alleviate these problems. Coevaporated B (p-type) has a simple incorporation mechanism by which good doping and profile control can be achieved using the conventional MBE technique of changing the source cell temperature. For n-type doping, a method of enhancing the low incorporation efficiency of Sb was found (potential enhanced doping) which is also ideally suited to profile control. Enhancements by a factor of up to 1000 times were achieved. Material with bulklike mobilities was obtained over the range of 1.times.10.sup.15 to 8.times.10.sup.19 cm.sup.-3 for p-type and up to 3.times.10.sup.19 cm.sup.-3 for n-type doping. Extremely sharp doping transitions down to &lt;100 .ANG./decade were obtained.
Other background references includes the following. U.S. Pat. No. 4,317,680 issued Mar. 2, 1982 to Chu et al entitled DIFFUSION SOURCE AND METHOD OF PREPARING, is directed to a diffusion source for establishing a p-type conductivity region in a semiconductor device and to a method for preparing such diffusion source. The diffusion source consists of pure silicon powder diffused with a p-type impurity.
U.S. Pat. No. 3,558,376 issued Jan. 26, 1971 to Schmidt et al entitled METHOD FOR CONTROLLED DOPING BY GAS OF FOREIGN SUBSTANCE INTO SEMICONDUCTOR MATERIALS, describes a controlled process for introducing foreign substances, e.g., dopants and recombination centers, into a molten semiconductor body by directing foreign substance in gaseous form in the immediate vicinity of the melt.
U.S. Pat. No. 3,949,119 issued Apr. 6, 1976 to Shewchen et al entitled METHOD OF GAS DOPING OF VACUUM EVAPORATED EPITAXIAL SILICON FILMS, describes a technique for the controlled incorporation of doping impurities into homoepitaxial silicon films by gas bombardment with arsine and diborane.
U.S. Pat. No. 4,447,276, issued May 8, 1984 to Davies et al entitled MOLECULAR BEAM EPITAXY ELECTROLYTIC DOPANT SOURCE, discloses a method of growing crystalline semiconductors such as GaAs. The method involves epitaxial deposition from the vapor phase and provides dopant material such as sulphur in the form of a molecular beam. The molecular beam is developed by effusion from a knudsen cell. The difficulties previously encountered using sulphur as such a cell are counteracted by use of an electrochemical cell as the sulphur source. The technique allow complicated doping profiles to be produced.